(1) Field of the Invention
The present invention relates to the technical field of radar detection systems. The present invention relates to an obstacle and terrain warning radar system for a rotorcraft and in particular for use in poor visibility due specifically to weather conditions.
(2) Description of Related Art
One of the main causes of rotorcraft accidents nowadays is contact while in flight with obstacles or indeed with the surrounding terrain. In particular, under unfavorable weather conditions or when flying at night, the risk of an accident is increased. Consequently, there is a major need for a warning system that enables the pilot of the rotorcraft to be alerted to the presence of one or more obstacles in the surroundings near to the rotorcraft, and also to the proximity of terrain. Such a warning system thus serves to avoid making contact with obstacles and terrain, if any, by warning the pilot of the rotorcraft. Such a warning system must be based on radar technology that is effective and reliable, and that is capable of guaranteeing such detection regardless of weather conditions.
Document DE 4 328 573 describes an all-weather vision system for a helicopter combining information coming from a rotating synthetic aperture radar (ROSAR) type radar with flight and navigation information in order to provide the pilot with artificial vision of the surroundings. That radar has transmitter and receiver elements situated on the rotor head of the helicopter and at the ends of a plurality of arms forming antennas, each positioned between a pair of blades of the main rotor. Those transmitter and receiver elements rotating with the main rotor are fastened on a central structure such as a turnstile and they are protected from aerodynamic forces and bad weather by a cover. However, the radar assembly presents heavy weight located above the main rotor, and also significant aerodynamic drag. In addition, as it is based on the synthetic aperture radar principle that all-weather vision system uses technology that is very complex and requires a powerful computer to handle the received data as well as to perform the rotating synthetic aperture algorithms.
In addition, document DE 10-2006/053354 describes a panoramic vision system for a helicopter having a plurality of radar sensors positioned at different locations on the helicopter fuselage in order to be capable of scanning the surroundings of the helicopter. The radar sensors operate with short-range and long-range wavelengths in order to, on the one hand, scan zones behind and beside the helicopter and, on the other hand, zones situated in front of the helicopter. The signals from those radar sensors are delivered to an evaluation and detection unit, and then the system displays the signals after they have been processed on display means situated in the cockpit, and information is compared with a predetermined warning threshold value. Each radar sensor needs to perform two-dimensional scanning, which requires complex antennas for performing electronic scanning in two dimensions. In addition, such a system requires numerous different sensor positions and an installation process that is complex.
Also known is document WO 2011/136707 that describes a laser obstacle detection and warning system for helicopters. That system emits laser light and receives laser light reflected by any obstacles located close to the helicopter. The system has a sensor unit having a plurality of obstacle detection sensors positioned on the rotor head of the helicopter and rotating with the main rotor, and also a warning unit and means for communicating between the sensor unit and the warning unit. The emitted laser light covers a sector volume around the axis of rotation of the main rotor. In that system, it is necessary for the laser to scan the surroundings mechanically in the vertical direction during high-speed rotation of the main rotor. However, that mechanism is prone to defects and has significant probability of failure. It consequently requires regular maintenance. Another drawback is that the laser presents a beam that is narrow and unsuitable for covering large areas.
Document U.S. Pat. No. 5,451,957 discloses a ROSAR system where the radar units are a plurality of antennae located at the end of a rotating arm (a blade or a turnstile), and wherein the scanning in elevation is carried out by the changeable orientation of the antennae. This system does therefore comprise movable parts that make it less reliable and robust.
Document DE 102006037898 describes a ROSAR system with a plurality of antennae, each antenna located at the tip of a rotor blade and having a different vertical orientation. Document U.S. Pat. No. 5,614,907 relates to a ROSAR radar sensor in which the transmit/receive antennae are located at the ends of the support arms of a turnstile.
Document “Miniaturized and low cost obstacle warning system” discloses a radar warning system wherein the aperture distribution of the radar, both in the azimuth and in the elevation direction, is achieved by using digital beam-forming techniques.
Finally, document JP 4 276 583 describes a system for detecting obstacles at long range by means of a laser and for use on helicopters. A laser source and receiver are placed on the shaft for driving rotation of the main rotor of a helicopter, the laser source emitting a spot beam of laser light and the receiver receiving the light reflected by any obstacle. On the rotary shaft, a position coder serves to determine the direction of a detected obstacle. That obstacle detection system is limited, enabling obstacles to be detected only in an azimuth direction around the axis of rotation of the main rotor of the helicopter and is therefore incapable of detecting obstacles in a height position, i.e. above or below the helicopter. In addition, since it uses a laser, it is subject to the same drawbacks as WO 2011/136707.